1. Field of the Invention
The present invention relates to an oil and grease analysis for wastewater, and more particularly, to recovery of solvent used in the oil and grease analysis.
2. Description of the Related Art
Wastewater discharged from industrial and municipal wastewater treatment plants is typically tested for oil and grease content. A standard method used in performing this test involves the intimate mixing of a sample of wastewater with a solvent for extracting oil and grease from the wastewater sample. The solvent presently used is heavier than water and readily separate from the water, settling to the bottom of the mixing vessel. As illustrated in FIG. 1, the mixing vessel used is typically a separatory funnel SF. The solvent and extracted oil and grease is filtered through a filter paper FP in a filter funnel FF and collected in a clean, dry collection flask CF of known weight. The solvent is evaporated in a hood H with solvent passing into the atmosphere via an exhaust opening EO, and the dry flask CF is then weighed again. The difference in the weight of flask CF is the oil and grease content, which remains in flask CF as a residue after the solvent is evaporated. The difference in the two weights, expressed as a ratio to the original sample weight, is the percentage of oil and grease in the wastewater.
Presently, the oil and grease tests are conducted according to United States Environmental Protection Agency (EPA) Methods 413.1 or 5520B. The solvent used for Methods 413.1 or 5520B is a trichlorotrifluoroethane specifically, 1,1,2-trichloro-1,2,2-trifluoroethane, available from E. I. DuPont de Nemours & Company under the registered trademark FREON (referred to hereinafter as "chlorofluorocarbon"). Chlorofluorocarbon has been widely used as an effective solvent useful in the determination of oil and grease because of its solvent power for oils, greases, waxes and the like. However, chlorofluorocarbons in the atmosphere have been identified as a primary contributor to the degradation of an ozone layer in the earth's upper atmosphere. Chlorofluorocarbon is also quite expensive. So ongoing wastewater analysis for oil and grease content is somewhat expensive because the chlorofluorocarbon is evaporated to the atmosphere.
U.S. Pat. No. 5,294,553, assigned on its face to the EPA, is incorporated by reference herein for all purposes. The '553 patent discloses a review of technology available for the gravimetric determination of oil and grease. The EPA has recently published a Method 1664 which replaces chlorofluorocarbon in oil and grease analysis, with hexane as the solvent. Paragraphs 6.6 and 11.4 of Method 1664 call for recovering solvent during solvent evaporation using a distilling head claisen, a distilling adapter and a solvent collection flask. However, in this Method 1664, before the step of evaporation, hexane is drained openly from a separatory funnel through a filter funnel into a boiling flask. During this filtration step, solvent evaporates into the atmosphere, which both potentially exposes the analyst to the vapors and contributes to solvent losses. Consequently, a need remains for an apparatus and method for conducting oil and grease analyses, while minimizing solvent losses to the atmosphere.